Moldable resin composition

ABSTRACT

A resin composition moldable at room temperature comprising a thermosetting unsaturated polyester resin, a mixture of thermoplastic polymers of vinyl acetate and an epoxy compound having at least one 1,2-epoxy group per molecule, a dialkyl-p-toluidine accelerator, a low temperature free radical peroxide initiator such as a blend of cumene hydroperoxide and acetyl acetone peroxide, and an alkali metal or transition metal compound capable of reacting with the free radical initiator to initiate polymerization of the unsaturated polyester resin.

FIELD OF THE INVENTION

This invention relates to a resin composition, and more particularly toan unsaturated polyester resin composition moldable at room temperature.

BACKGROUND OF THE INVENTION

Unsaturated polyester resins, and particularly reinforced unsaturatedpolyester resins have wide commercial utility in manufacturing suchitems as automotive parts, boat hulls, bath and kitchen fixtures (e.g.,sink basins, vanity tops, shower units, etc.), aerospace parts, storagetanks and the like. Various fabrication techniques can be used,including among others, hand lay-up, matched metal-die molding,compression molding including the use of sheet molding compound ("SMC")and bulk molding compound ("BMC"), transfer molding, injection molding,and resin transfer molding ("RTM"). Unsaturated polyester resins oftenhave to be cured at elevated temperatures (e.g., temperatures greaterthan about 40° C. and often greater than about 120° C.) to gain thedesired properties, and particularly the desired surface properties.Exposure to elevated temperatures, however, is often detrimental to thequality of the resulting molded article. Moreover, expensive toolingmade from heat resistant materials (e.g., steel and chrome) and havingmeans for providing heat to the tool often have to be utilized.

Molding at elevated temperatures is usually required when attempting tomold articles (e.g., automotive exterior parts) that require a smoothsurface quality, known as Class A surfaces, and exhibit reducedshrinkage and warpage. When molding Class A articles, compressionmolding techniques are conventionally used in conjunction with a lowprofile additive added to the resin. See, for example, U.S. Pat. Nos.4,525,498 to Atkins et al., 4,172,059 to Atkins et al., and 3,701,748 toKroekel.

Despite the general availability of unsaturated polyester resins usingsuch additives, there continues to be a need for improvements in moldingresins, and particularly molding unsaturated polyester resins at roomtemperature. Resins that cure (mold) at room temperature have heretoforenot been entirely successful when used in molding Class A articles.Conventional thinking is that elevated molding temperatures (e.g., onthe order of 120° C. to 160° C.) are necessary to obtain Class Asurfaces.

SUMMARY OF THE INVENTION

With the foregoing in mind, it is an object of the invention to providean unsaturated polyester resin composition which is moldable at roomtemperature.

It is another object of the invention to provide an unsaturatedpolyester resin composition which is moldable at about room temperatureusing compression molding and RTM techniques.

It is still another object of the invention to provide an unsaturatedresin composition which is moldable at room temperature and provides anarticle having Class A surface quality.

These and other objects of the invention are provided by the resincomposition of the present invention. It has been discovered that aresin composition comprising a thermosetting unsaturated polyesterresin, a mixture of thermoplastic polymers of vinyl acetate and an epoxycompound having at least one 1,2-epoxy group per molecule, adialkyl-p-toluidine accelerator, a free radical initiator comprising alow temperature free radical peroxide initiator such as methyl ethylketone peroxide, benzoyl peroxide, t-butyl hydroperoxide and othersknown in the art, and particularly a blend of cumene hydroperoxide andacetyl acetone peroxide, and an alkali metal or transition metalcompound capable of reacting with the free radical initiator to initiatepolymerization of the unsaturated polyester resin can be molded at orabout room temperature (i.e., at temperatures of about 20° C. to about40° C.) to give Class A surfaces and low shrinkage. Preferably, thetransition metal compound is cobalt naphthenate or cobalt octoate.

Additionally, the resin composition can include fillers (e.g., calciumcarbonate, alumina powder, hydrated alumina, quartz powder, crushedsilica, etc.) and/or reinforcement fibers (e.g., fibers of glass,carbon, aromatic polyamides, etc.). The present resin composition isunlike existing resin compositions in that the resin composition can bemolded at room temperature and can still be used to provide Class Asurface quality.

The present invention also relates to a method of producing a moldedarticle comprising the steps of forming a resin composition comprising athermosetting unsaturated polyester resin, a mixture of thermoplasticpolymers of vinyl acetate and an epoxy compound having at least one1,2-epoxy group per molecule, a dialkyl-p-toluidine accelerator, a lowtemperature free radical peroxide initiator such as a blend of cumenehydroperoxide and acetyl acetone peroxide, and an alkali metal ortransition metal compound capable of reacting with the free radicalinitiator to initiate polymerization of the unsaturated polyester resin,forming a shaped article from the resin composition, and subjecting theshaped article to a temperature of about 20° C. to about 40° C. topolymerize the thermosetting unsaturated polyester resin to provide amolded article having a Class A surface and low shrinkage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more fully hereinafter. Thisinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiment set forth herein; rather,this embodiment is provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art.

As summarized above, the resin composition of the present invention ismoldable (curable) at room temperature. The resin composition comprisesa thermosetting unsaturated polyester resin, a mixture of thermoplasticpolymers of vinyl acetate and an epoxy compound having at least one1,2-epoxy group per molecule, dialkyl-p-toluidine accelerator, a freeradical peroxide initiator (e.g., a blend of cumene hydroperoxide andacetyl acetone peroxide), and an alkali metal or transition metal saltcapable of reacting with the free radical initiator to initiatepolymerization of the unsaturated polyester resin.

Preferably, the resin composition comprises about 50 to about 75 percentby weight of thermosetting unsaturated polyester resin; about 5 to about15 percent by weight of the mixture of thermoplastic polymers of vinylacetate and the epoxy compound having at least one 1,2-epoxy group permolecule, about 0.05 to about 0.5 percent by weight dialkyl-p-toluidineaccelerator, about 0.5 to about 3 percent by weight of the free radicalperoxide initiator, and about 0.05 to about 0.5 percent by weight of thealkali metal or transition metal salt capable of reacting with the freeradical initiator to initiate polymerization of the unsaturatedpolyester resin. Additionally, the resin composition can includefillers, inhibitors, reinforcement fibers and the like.

Suitable unsaturated polyester resins include practically anyesterification product of a polybasic organic acid and a polyhydricalcohol, wherein the acid provides the ethylenic unsaturation. Typicalunsaturated polyesters are those thermosetting resins made from theesterification of a dihydric alcohol with an ethylenically unsaturateddicarboxylic acid. Examples of useful ethylenically unsaturatedpolycarboxylic acids include maleic acid, fumaric acid, itaconic acid,dihydromuconic acid, and halo and alkyl derivatives of such acids andanhydrides, and mixtures thereof. Exemplary polyhydric alcohols includesaturated polyhydric alcohols such as ethylene glycol, 1,3-propanediol,propylene glycol, 2,3-butanediol, 1,4-butanediol,2-ethylbutane-1,4-diol, 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol,2,10-decanediol, 1,4-cyclohexanediol, 1,4-dimethylolcyclohexane,2,2-diethylpropane-1,3-diol, 2,2-dimethylpropane-1,3-diol,3-methylpentane-1,4-diol, 2,2-diethylbutane-1,3-diol, 4,5-nonanediol,diethylene glycol, triethylene glycol, dipropylene glycol, glycerol,pentaerythritol, erythritol, sorbitol, mannitol,1,1,1-trimethylolpropane, trimethylolethane, hydrogenated bisphenol-Aand the reaction products of bisphenol-A with ethylene or propyleneoxide.

The unsaturated polyester resins are generally crosslinked with acompatible crosslinking monomer such as styrene, vinyl toluene, methylmethacrylate, methyl styrene, divinyl benzene, diallyl phthalate and thelike. The amount of crosslinking monomer is about 10 percent to about 65percent, and preferably about 25 percent to about 55 percent by weightof the unsaturated polyester resin.

The polyester resin can also be mixed or blended with otherthermosetting resins. For example, the polyester resin can be mixed witha crosslinkable polyurethane such as described in U.S. Pat. No.4,062,826 to Hutchinson et al, the disclosure of which is incorporatedherein by reference. The use of other thermosetting resins and blendsthereof will be within the skill of one in the art.

Exemplary mixtures of thermoplastic polymers of vinyl acetate and ofepoxy compounds having at least one 1,2-epoxy group per molecule aredescribed in U.S. Pat. No. 4,525,498 to Atkins et al., the disclosure ofwhich is incorporated herein by reference. Suitable thermoplastic vinylacetate polymers are polyvinyl acetate homopolymers and thermoplasticcopolymers containing at least 50 percent by weight vinyl acetate. Suchpolymers include, for example, vinyl acetate homopolymer; carboxylatedvinyl acetate polymers including copolymers of vinyl acetate andethylenically unsaturated carboxylic acids, such as acrylic acid,methacrylic acid, maleic acid, fumaric acid, itaconic acid and the likeor anhydrides such as maleic anhydride; vinyl acetate/vinylchloride/maleic acid terpolymer, and the like. The useful vinyl acetatepolymers typically have molecular weights within the range of from about10,000 to about 250,000, and preferably from about 25,000 to about175,000.

Suitable epoxy compounds having at least one 1,2-epoxy group permolecule can be based on aliphatic, cycloaliphatic or aromaticbackbones. One class of preferred thermosetting epoxy resins can berepresented by the formula: ##STR1## wherein n is an integerrepresenting the number of repeating units and has a value of 0 to about10 and Z is an arylene radical having 6 to about 20 carbons. Thepreferred arylene radical is: ##STR2## Still another preferred class ofthermosetting epoxy resins are the 1,2-cycloaliphatic diepoxides such as3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate,bis(2,3-epoxycyclopentyl)ether, vinyl cyclohexane dioxide, and2-(2,4-epoxycyclohexyl-5,5-spiro)-(3,4-epoxy)cyclohexane-m-dioxane. Itis noted that the mixture has previously been used as a low profileadditive ("LPA") in molding articles to reduce volume shrinkage such asdescribed in U.S. Pat. No. 4,525,498 to Atkins, et al.

Exemplary dialkyl-p-toluidine accelerators are dimethyl-p-toluidine,diethyl-p-toluidine and the like. The dimethyl-p-toluidine acceleratoris preferred and is available, for example, from RSA Corporation ofArdsley, N.Y.

Suitable free radical peroxide initiators include t-butyl hydroperoxide,t-butyl perbenzoate, benzoyl peroxide, methyl ethyl ketone peroxide, andothers known in the art. Preferred initiators are methyl ethyl ketoneperoxide and a blend of cumene hydroperoxide and acetyl acetoneperoxide. The blend of cumene hydroperoxide and acetyl acetone peroxideis typically about a 1:1 to about 1:9 blend, with a blend of from about1:4 to 1:5 cumene hydroperoxide to acetyl acetone peroxide beingpreferred.

Exemplary alkali metal and transition metal salts capable of reactingwith the free radical initiator to initiate polymerization includeacetate, butyrate, benzoate, capronate, laurate, palmitate, octoate,propionate and naphthenate salts of Na, K, Li, Pb, Fe, Co, Ni, Zn and V.A preferred transition metal salt is cobalt naphthenate or cobaltoctoate.

The resin composition can also include an inhibitor to give shelfstability and adjust gel time. Exemplary inhibitors include tertiarybutyl catechol, hydroquinone, p-benzoquinone, monotertiary butylhydroquinone, 1,4-napthoquinone, toluhydroquinone, anddi-tert-butyl-p-cresol. Preferably, the amount of inhibitor in the resincomposition ranges from about 0.05 to about 0.5 percent by weight.

The resin composition can optionally include a filler such as calciumcarbonate (e.g., SnowFlake available from ECC America, Inc. ofSylacauga, Ga.), alumina powder, hydrated alumina, quartz powder,crushed silica, calcium sulfate, kaolin, talc and the like. Preferably,the amount of filler in the resin composition ranges from about 25 toabout 200 percent by weight.

The resin composition optionally can include reinforcement fibers.Suitable reinforcement fibers include fibers of glass, carbon, aromaticpolyamides, ceramic and various metals. The fibers are used in amountsof about 5 to about 75 percent, and preferably about 20 to 60 percent byweight based on the weight of the resin composition. Also, a veil matcan be used.

A suitable resin composition is Polylite® 31-520 available fromReichhold Chemicals, Inc. Polylites® 31-520 is a mixture of unsaturatedpolyester resins having a very high ethylenic unsaturation, XLPR-85D44(a mixture of thermoplastic vinyl acetate and epoxy compound having atleast one 1,2 epoxy group per molecule available from Union Carbide,Charleston, W. Va.), dimethyl-p-toluidine accelerator, a blend of cumenehydroperoxide and acetyl acetone peroxide, cobalt octoate promoter, andtertiary butyl catechol inhibitor.

In operation, the resin composition is formed by mixing together theindividual constituents and forming the composition into a shapedarticle using any of the various known molding techniques (e.g., handlay-up, compression molding, RTM, and the like). The resin compositionis molded at room temperature or slightly above (e.g., of about 20° C.to about 40° C.) at a pressure of about 1 atm to about 100 atm to formthe molded article with or without vacuum assist to get the resin in themold.

Additional benefits and advantages of the invention will be apparent inthe following illustrative example. Unless otherwise noted, all partsand percentages are by weight of the resin composition.

EXAMPLE

A paste mixture of the resin composition is prepared comprising 100parts by weight Polylites® 31-520 which comprises:

a. 87 parts by weight styrenated unsaturated polyester resin having ahigh ethylenic unsaturation,

b. 13 parts by weight Union Carbide XLPR-85D44, a styrenated mixture ofthermoplastic polymers of vinyl acetate and an epoxy compound having atleast one 1,2 epoxy group per molecule,

c. 0.4 parts by weight dimethyl-p-toluidine accelerator,

d. 1.25 parts by weight of a 1:4 blend of cumene hydroperoxide andacetyl acetone peroxide, and

e. 0.4 parts by weight cobalt octoate; 100 parts by weight calciumcarbonate; and 35 parts by weight of glass made up of 10 mil Veil backedup with 11/2 oz. chopped strand glass fiber mat available fromNicofibers Inc. of Shawnee, Ohio. The gel time of the mixture is about 4minutes and the mix temperature is about 27° C. The paste mixture isplaced in a polyester mold coated with a release wax. Each layer ofglass fiber mat is laid out, wet with the paste mixture, and rolled cutwith a hand lay up roller. Multiple layers are wet out until a thicknessof 125 mil is obtained. The paste mixture is permitted to cure at roomtemperature (i.e., 25° C.) for about 1/2 hour. The SPI gel time (60° C.)is 1 minute and 19 seconds, the SPI cure time (60° C.) is 1 minute and10 seconds, and the peak exotherm temperature (PET) is 370° F. (188°C.). The high PET contributes to the low shrinkage of the article. Theresulting molded article has a shiny appearance and good surfacesmoothness. The article has a good shrinkage percentage of -0.21% (i.e.,it expands).

COMPARATIVE EXAMPLE

A paste mixture of a resin composition is prepared as in Example 1except no dimethyl-p-toluidine is included. The resulting molded articleis dull and has poor surface smoothness. The article has a Doorshrinkage percentage of -0.07% (i.e., less expansion).

In the specification and example, there have been disclosed preferredembodiments of the invention, although specific terms are employed, theyare used in a generic and descriptive sense only and not for the purposeof limitation, the scope of the invention being defined by the followingclaims.

We claim:
 1. A resin composition moldable at room temperaturecomprising:(a) a thermoplastic unsaturated polyester resin; (b) amixture of thermoplastic polymers of vinyl acetate and an thermosettingepoxy compound having at least one 1,2-epoxy group per molecule; (c) adialkyl-p-toluidine accelerator; (d) a low temperature free radicalperoxide initiator; and (e) a transition metal compound capable ofreacting with the free radical initiator to initiate polymerization ofthe unsaturated polyester resin.
 2. A resin composition according toclaim 1 including an inhibitor selected from the group consisting oftertiary butyl catechol, hydroquinone, p-benzoquinone, monotertiarybutyl hydroquinone, 1,4-naphthoquinone, toluhydroquinone, anddi-tert-butyl-p-cresol.
 3. A resin composition according to claim 1wherein the free radical initiator is a blend of cumene hydroperoxideand acetyl acetone peroxide.
 4. A resin composition according to claim 1wherein the free radical initiator is methyl ethyl ketone peroxide.
 5. Aresin composition according to claim 1 including a filler selected fromthe group consisting of calcium carbonate, alumina powder, hydratedalumina, quartz powder, crushed silica, calcium sulfate, kaolin, andtalc.
 6. A resin composition according to claim 1 wherein the transitionmetal salt capable of reacting with the free radical initiator toinitiate polymerization of the unsaturated polyester resin is cobaltnaphthenate or cobalt octoate.
 7. A resin composition according to claim1 wherein the dialkyl-p-toluidine accelerator is dimethyl-p-toluidine.8. A fiber-reinforced resin composition moldable at room temperaturecomprising:(a) about 50 to 75 percent by weight of thermosettingunsaturated polyester resin; (b) of a mixture of thermoplastic polymersof vinyl acetate and an thermosetting epoxy compound having at least one1,2-epoxy group per molecule; (c) about 0.05 to about 0.5 percent byweight dimethyl-p-toluidine accelerator; (d) about 0.5 to about 3.0percent by weight of a low temperature free radical initiator comprisinga blend of cumene hydroperoxide and acetyl acetone peroxide; (e) about0.05 to about 0.5 percent by weight of a cobalt salt capable of reactingwith the free radical initiator to initiate polymerization of theunsaturated polyester resin; and (f) about 10 to about 40 percent byweight of a reinforcement fiber.
 9. A resin composition according toclaim 8 including an inhibitor selected from the group consisting oftertiary butyl catechol, hydroquinone, p-benzoquinone, monotertiarybutyl hydroquinone, 1,4-naphthoquinone, toluhydroquinone, anddi-tert-butyl-p-cresol.
 10. A resin composition according to claim 8including a filler selected from the group consisting of calciumcarbonate, alumina powder, hydrated alumina, quartz powder, crushedsilica, calcium sulfate, kaolin, and talc.
 11. A resin compositionaccording to claim 8 wherein the cobalt salt capable of reacting withthe free radical initiator to initiate polymerization of the unsaturatedpolyester resin is cobalt naphthenate or cobalt octoate.
 12. A resincomposition according to claim 8 wherein the reinforcement fiber isselected from the group consisting of fibers of glass, carbon, aromaticpolyamides, ceramic and metal.
 13. A shaped article comprising thecomposition of claim 8.